Process for recovery of vanadium values from ferrophosphorus and/or ferrophosphorus mixture

ABSTRACT

A CANADIUM EXTRACTION PROCESS COMPRISING THE ROASTING OF A MIXTURE OF PREOXIDIZED FERROPHOSPHORUS WITH OR WITHOUT A VANDIUM-CONTAINING ORE, AN ALKALINE EARTH MATERIAL AND AN ALKALINE METAL SALT. THE CALCINED MIXTURE IS THEN LEACHED IN AN AQUEOUS SOLUTION AND THE LEACH LIQUOR SO FORMED IS THEREAFTER FILTRATED TO EXTRACT THE VANADIUM VALUES THEREIN.

United States Patent Int. Cl. C01g 31/00 US. Cl. 42368 13 ClaimsABSTRACT OF THE DISCLOSURE A vanadium extraction process comprising theroasting of a mixture of preoxidized ferrophosphorus with or without avanadium-containing ore, an alkaline earth material andan alkaline metalsalt. The calcined mixture is then leached in an aqueous solution andthe leach liquor so formed is thereafter filtrated to extract thevanadium values therein.

This application is a continuation-in-part of U.S. Ser. No. 124,484,filed Mar. 15, 1971, now abandoned.

FIELD OF THE INVENTION This invention relates to a roasting-leachingprocess for extracting vanadium values from ferrophosphorus and/orferrophosphorus mixtures using preoxidized ferrophosphorus an alkalineearth material and an alkaline metal salt.

DESCRIPTION OF PRIOR ART Numerous efiorts have been made to extractvanadium values from raw material containing the same but because of thecomplexity of the processes involved, no completely satisfactory processhas been developed. In addition to the vanadium values present in rawmaterials such as phosphate rock located throughout a number of westernand southern states, a relatively sizable amount of vanadium iscontained in ferrophosphorus, which is produced as a by-product in themanufacture of elemental phosphorus. One approach for recoveringvanadium values from vanadium-containing ferrophosphorus consists in thefusion of ferrophosphorus in the presence of excess oxygen and an alkalimetal halide. The vanadium is then extracted by a conventional leachingtechnique using an aqueous solvent. Another approach employed torecovering vanadium from iron-base alloys is to charge a mixture offerrophosphorus, iron oxide and silicon into an electric furnace to forma molten alloy and a vanadium-containing slag. The slag so formed isthen mixed with an alkali halide and thereafter conventionally roastedto recover the vanadium.

Although these processes have resulted in the recovery of vanadium tosome extent from vanadium-containing ferrophosphorus, they entail theuse of complex process steps and/ or expensive operating equipment. Thepresent invention is directed to the substantial recovery of vanadiumvalues contained in ferrophosphorus, and/or ferrophosphorus mixed withother vanadium-containing ores by a process admirably suited forcommercial application.

SUMMARY OF THE INVENTION This invention relates to a roasting-leachingprocess for recovering vanadium values from ferrophosphorus and/ orferrophosphorus mixed with other vanadium-containing materials. Theprocess basically consists of a two stage oxidation of ferrophosphorous;the first stage involves heating particulated ferrophosphorous in air ata temperature in the range of about GOO-750 C. for about 15 min- "iceutes to two hours. A suitable sizing for-the particulatedferrophosphorous in the first stage is about 20 to X150 mesh. In thesecond stage the partially oxidized ferrophosphorous is heated in air inthe range of about 800- 900" C. for about /2 hour to 5 hours. In thesecond stage the partially oxidized ferrophosphorous can be particulatedto -50 to +270 mesh. The thus preoxidized ferrophosphorus is mixed withan alkaline earth containing material and an alkaline metal salt and themixture roasted. The roasted mixture is then subjected to a leachingprocess using an aqueous solvent to dissolve the vanadium values thereinwhereupon the leach liquor can then be appropriately filtered to recoverat least of the vanadium values contained in the original oxidizedferrophosphorus.

One possible procedure for oxidizing ferrophosphorus is to firstpulverize the ferrophosphorus by any conventional technique to produce aparticulated form. The particulated ferrophosphorus can then besubjected to an oxidizable environment for time periods and temperaturesas described above sufficient to substantially convert the phosphorus tothe phosphate compound. Any oxidants can be employed for this purposeincluding such methods as hearth oxidation, fluid-bed oxidation,rotary-kiln oxidation, flame oxidation and the like.

The substantially oxidized ferrophosphorus is then mixed with at leastone alkaline earth containing material, such as calcium carbonate (CaCOcalcium oxide (CaO), magnesium carbonate MgCO magnesium oxide (MgO),alkaline earth-containing slags, alkaline earthcontaining ores, or thelike and at least one alkaline metal salt, such as sodium chloride(NaCl), potassium chloride (KCl), sodium carbonate (Na CO sodiumsulfate. (Na SO or the like, preferably sodium chloride. The exact moleratio of the alkaline earth material, such as CaCO to phosphorus in theoxidized ferrophosphorus is somewhat critical and should be betweenabout 1.0 and about 2.0, preferably about 1.5. This is required tosubstantially insure the following reaction:

The amount of the alkaline metal salt, such as NaCl, which is to beadded to the mixture of preoxidized ferrophosphorus plus the alkalineearth containing material is variable although a percentage betweenabout 3. and about 35 based on the weight of the mixture is suitable,and between about 10 and about 25 is preferable.

The temperature and time period for the roasting cycle are variablebeing between about 700 C. and about 1050 C. for a resident time of atleast 45 minutes. A temperature of between about 850 C. and about 950 C.held for a time period of about 1 hour or more is desira'ble for theroasting cycle while a temperature about 875 C. for a time period ofbetween about 1 and about.

2 hours is preferable. During the roasting cycle the vanadium in theferrophosphorus is believed to be converted to sodium v'anadate therebymaking the vanadiumvalues amenable to dissolution in a liquid medium.

The aqueous solvent required for the leaching stage should be ofsuificient quantity to dissolve the vanadium values in the roastedmixture whereupon the aqueous leach liquor can then be filtered byconventional techniques to separate the vanadium values therein.

The preferred method for implementing this invention is to initiallypulverize ferrophosphorus into a particulated form and then oxidizing itwith a sufficient amount of an oxidant to convert the phosphorus thereinthe phos phate state. The oxidized ferrophosphorus thereafter is mixedwith an alkaline earth material in a mole ratio with the phosphorus inthe oxidized ferrophosphorus off about 1.5. For example, when CaO isused as the alkaline earth material, a 1.5 ratio will be sufiicient tosubstantially satisfy the following reaction:

An alkaline metal salt, such as NaCl, is then added to the mixture ofthe oxidized ferrophosphorus and alkaline earth additive, in an amountequal to about 25% of the Weight of the mixture. The composite so formedis intermixed with water, compacted into predesired shapes and thensubjected to a roasting process wherein it is heated to a temperature ofabout 875 C. and held thereat for a time period of about 2 hours. Duringthe roasting period the vanadium present in the mixture is believed to-be converted into sodium vanadate so that when the mixture is leachedin an aqueous solution, the vanadium values therein will substantiallydissolve. The leach liquor is then filtered by any conventionaltechnique to separate the vanadium values therein. This roasting andleaching process will result in the extraction of at least 85% of thevanadium values therein. This roasting and leaching phorus.

It is also within the purview of this invention to add oxidizedferrophosphorus to other vanadium-containing ores and then process themixture according to the above procedure to extract the vanadium valuestherein.

EXAMPLE 1 A sample of ferrophosphorus was obtained from an electricfurnace smelting process wherein phosphate rock was charged to produceelemental phosphorus. The ferrophosphorus, a by-product of the aboveprocess, was pulverized to 100 Tyler mesh size and finer and thenanalyzed by chemical and spectrographic analyses which revealed a Vcontent of 8. 86%, a P content of 25.4% and a Fe content of 57.2%.

A A; inch thick layer of the particul-ated ferrophosphorus was spread ona silica dish and then placed in a mufile furnace. The temperature inthe furnace was raised to 700 C. and held thereat for 3 hours while Wetair flowed over the bed. The ferrophosphorus was thereafter removed andupon being cooled to ambient it was weighed and found to have gained 5%in weight. The ferrophosphorus was again pulverized and spread on a 4silica tray and this time heated overnight at an elevated temperature of825 C. Again wet air was forced to flow over the bed. Upon removal fromthe furnace and cooling to ambient, the ferrophosphorus was weighed andfound to have gained 63% in weight, such gain being attributed to theoxidation of the ferrophosphorus which was present predominantly asFePO; based on an X-ray study. Thus every gram of unoxidized FePproduced about 1.63 grams of oxidized FeP based on the above weightincrease. An analysis of the oxidized ferrophosphorus showed it tocontain 5.4% V 0 and 15.6% P.

A sample of ore, obtained from a composite of core drillings from anArkansas vanadium mine in Hot Springs, Arkansas, was pulverized, blendedand then upon being chemically and spectrographically analyzed, found tocontain Of V205.

Various mixtures of the oxidized and/or unoxidized ferrophosphorus, theArkansas ore, CaCO NaCl and water were blended and fed into a 1-inchdiameter cylindrical mold. A pressure of 1000 pounds was applied on a2.5-inch diameter ram which in turn compressed a 1-inch ram in the moldto produce l-inch diameter by 3- inch length wet compacts. Each compactwas thereupon placed in an alundum combustion boat and the assemblyinserted in a mufile furnace set at 875 C. with a wet air over bed.After a residence time of 2 hours in the furnace, the calcined compactwas removed, cooled to ambient and then crushed to Tyler mesh size andfiner. The pulverized material so formed was leached in boiling waterfor one hour after which the leach liquor was filtered. The residue andthe filtrate so obtained was chemically analyzed for V 0 and from thisanalysis the percent of V 0 extraction was calculated.

Following the procedure outlined above, six tests were conducted onmixtures having various proportions of the additives listed above. Tests5 and 6 were performed without the addition of pre-oxidized FeP and test'1 was performed without the addition of CaCO The result of all thetests are shown in Table 1 and by comparing the percent of V 0 extractedfrom each test sample, we see that the extractions according to theprocess of this invention are substantially higher than that of theprior art.

TABLE 1 [Water-soluble vanadium from a NaCl roast of Arkansas ore andferrophosphorus (reagent CaCO; when used)] Test No.

Item No. Description of item 1 2 3 4 5 6 1- Grams of Arkansas ore insample 60 60 6O 6O 60 2- Grams of oxidized FeP in sample. 9. 8 9. 8 9. 89. 8 0 2 Grams of unoxidized Fe? in sample 0 0 0 6. 0 6. 0 4 Grams ofreagent 09.00: 0 2. 6 7. 2 10. 2 0 7. 0

Item 2 5.. Percent oxidized FeP= X 16. 3 16. 3 16. 3 16. 3 0 0 Item 1Item 3 6 Percent unoxidized FeP= X100 0 0 0 0 10 10 Item 1 Item 4 7-Percent (320 O; added- 100 0 4. 3 12 17 0 12 Item 1 Moles of CaCO; inItem 4 8 Mole ratio of (CaC O /P) 0 0. 53 1. 5 2. 1 0 1. 5

Moles of P in FeP sample 7 9 Grams of NaCl added- 17. 2 18. 3 19. 3 20.0 16. 5 18.3

(Item 9) 1O Percent NaCl added=--- 100 25 25 25 25 (Item 1+Item 2+Item4) (Item 9) 11 Percent NaCl added=---100 (Item l-l-Item 3+Item 4) 25 25(g. V205 in Item 1+Item 2) 12- Percent V205 in sample=------- 1. 72 1.66 15. 6 1. 50

1 (Wts. of Item 1+Item 2+Item 4) (g. V205 in Item 1+Item 3) 13- PercentV205 in sample=--- 1. 82 1. 64

(Wts. of Item l-l-Item 3+Item 4) 14 Percent V205 extracted 60 69 88 8126 15 Percent V205 in tailings of leached residue 0. 73 0. 55 0. 210.32 1. 28

5 EXAMPLE II A second series of tests were conducted following theprocedure outlined above and using the same Arkansas Ore andferrophosphorus as prepared in Example I. The only deviation in thisseries of tests was the substitution of CaO for CaCO as the alkalineearth compound. Again several tests were performed without the oxidizedferrophosphorus additive. The results of this series of tests are shownin Table 2 and from an evaluation of the percent of V extracted fromeach test sample we see that the extraction according to the process ofthis invention is substantially higher than that of the prior art. Inaddition, large amounts of oxidized ferrophosphorus can be added tovanadium-containing ores without decreasing the percent extraction ofvanadium while increasing the amount of unoxidi'zed ferrophosphorus to avanadiumcontaining ore will substantially decrease the percentextraction of vanadium.

These tests also show that the best extraction of 89% V 0 was obtainedwith a mole ratio of Ca() to phos phorus of 1.5 which satisfies thereaction pacts were subjected to a roast-leach process as described inExample I. The percent of V 0 extracted from these tests varied from84%to 87% as shown in Table 3. These tests show that a high extraction ofvanadium is possible using MgCO or MgO as the alkaline earth compound inthe process of this invention.

TABLE 3 [Water-soluble vanadium from NaCl roast of Arkansas ore,ierrophosph'orus and MgO o'r MgCO's'l' 1 -inch diarneter wet compactswere prepared as'described in Example I using various proportions ofoxidized ferrophosphorus with Arkansas ore, a 1.5 mole ratio of CaCO permole of phosphorus in' th'eoxidized TABLE 2 [Watersoluble vanadium froma NaCl roast of Arkansas ore, ferrophosphorus and 080] Test No.

Description 1 I 2 i 3 5 V 6 7 8 9 Grams of Arkansas ore in samnle 50 5050 50 50 40' 40 40 Grams of oxidized Fe? in samlp 8. 2 8.2 8.2 16.4 16.416.4 0 0 0 Grams ofunoxidized FeP in sample... 2. 0 4. 0 6. 0 GramsoiCaO2.6 3.4 4.3 5.2 6.9 8.6 1.34 2.7 4.0

. Item 2 16.4 16.4 16. 4 32. 8 32:8 32. 8 5 Percent oxidized FeP= X100Item 1 Item 3 0 0 0 0 0 0 5 10 15 6 Percent uuoxidized FeP= X100 Item 1Moles of CaO in Item 4 1. 1 1. 5 1. 9 1. 1 1. 5 1. 9 1. 5 1. 5 1 5 7Mole ratio CaO/P Moles of P in FeP Sample 8 Grams of NaCl add 15. 2 15.415. 6 17. 9 18.3 18.8- 10.8 11.6 12. 5

(Item 8) 25' 25 25 25 25 25 9 Percent NaCl added-'-"'--100 (Item 1 Item2 Item 4) (Item 8) '25 25 25 10 Percent NaCl added= -100 (Item 1 Item 3+Item 4) (g. V205 if: Iteffi 1 g. V205 in Item 2) 1.64 1.62 1.59 2.021.98 1. 94 11 Percent V205 in samplw 100 (g. of Item 1 g. of Item 2 Item4) p (g. V20 in Item 1 g. V205 in Item 3) 1. 43 1.71 1. 95 12 PercentVzO -in saint 1 (g. or Item 1 g. of Item 3 Item 4) 13 Percent V205extracted..- 9 v 85 89 89 87 89 85 78 77 29 14 Percent V205 in tailingsoi leached residue 0. 26 0.20 0.20 0.29 v r 32 0.40 0. 49

EXAMPLE III ferrophosphorus and 25% by weight of NaCl based on A seriesof NaCl roast tests were performed as de-' scribed in Example 1 exceptthat MgCO or MgO was used as the alkaline earth compound instead of CaCOUsing the same Arkansas ore and oxidized fer-rophosphorus as prepared inExample I and mixed with a ratio of 32.5 grams of oxidizedferrophosphorus to every 100 grams of Arkansas ore, 1 inch diameter wetcompacts were prepared. Also included in the wet compacts were variousmole ratios of Mg'CO to P or MgO to P and 25% by weight NaCl as based onthe total weight of ore, oxidized ferrophosphorus and either MgCO orMgO. These comsignificantly without impairing the vanadium extraction.

TABLE 4 [Water-soluble vanadium resulting from NaCl roast of Arkansasore and/or ferrophosphorus plus CaCOa] Test No.

Item N Description of item 1 2 3 4 5 6 1.. Gram of Arkansas ore insample-.. 50 50 40 20 10 0 2. Gram of oxidized FeP in sample 12. 2 16. 326. 1 32. 6 48. 9 40 3 Gram of reagent 02.00: in sizfipley 9. 1 12. 219. 6 24. 5 36. 7 30 em 4 Percent oxidized FeP 19. 6 24. 5 39. 5 62 083. 0 100 (Item 1 Item 2) (Gram V205 in Item 1 Item 2 5 Percent V205 insample=---1 1. 70 1. 84 2. 18 2. 59 2. 91 3. 12

(Wt. of Item 1 Item 2 Item 3) 6 Percent V205 in tailiugs of leachedresidue 0. 18 0. 20 O. 26 0. 27 0. 34 0. 44

I (g. V205 in residue X100) 7 Percent V105 extraeted=100- 91 91 90 92 9189 (g. V105 in sample) EXAMPLE V Table 7. Again maximum recovery of V 0was obtained l-inch diameter wet compacts, prepared as described inExample I from 32.5 grams of oxidized ferrophosphorus per 100 grams ofArkansas ore, 1.5 moles of CaCO per mole of P in the oxidizedfer-rophosphorus, and 25 by weight of NaCl based on the weight of theore, oxidized ferrophosphorus and CaCO were subjected to a roastleachprocess as outlined in Example I. The roast temperature was varied from725 C. to 1025 C. for several samples while the residual time was heldconstant at 2 hours. The percent of V 0 extracted from the compacts forthe different roasting temperatures is tabulated in Table 5 and showsthat maximum vanadium recovery was had at about 875 C.

TABLE 5 [Eflect of temperature on NaCl roast of Arkansas ore mixed withoxidized ferrophosphorus plus l-inch diameter wet compacts, prepared asin Example I from oxidized ferrophosphorus, 1.5 moles of CaCO per moleof P in the oxidized ferrophosphorus and various percentages of NaClbased on the weight of the ferrophosphorus and the CaCO were subjectedto a roastleach process as described in Example I. The eifect of theNaCl additive on the V 0 extraction is shown in Table 6. The resultsobtained demonstrate that excellent extractions can be had with a 25% byweight NaCl addition. Higher amounts of NaCl probably will not reducethe extraction of vanadium but will lower the vanadium throughput in theroasting step.

TABLE 6 [Eflect of amount of NaCl on roast of oxidized ierrophosphorusplus CaCOa] Percent V20; Percent NaCl Extrac- In Test No added tionresidue EXAMPLE VII at 875 C.

TABLE 7 [Effect of temperature on NaCl roast of oxidized ierrophos plusCaOOa] Percent V20:

Roast temp. Extrac- Test No. 0.) tion residue EXAMPLE VIII TABLE 8[Efiects of amount of NaCl on roast of Arkansas ore, oxidizedferrophosphorus plus 09.0 0:]

Percent V10: Percent NaCl Extrac- In Test No. added tion residue EXAMPLEIX Slag obtained from an open hearth furnace in Chile was chemicallyanalyzed and found to contain 5.85% V 0 1.38% P, 19.6% CaO, 5.7% MgO,30.7% Fe and various other impurities. Ferrophosphorus, upon beingchemically analyzed, was found to contain 23.8% P, 5.3% 0 and 6.53% V 0while oxidized ferrophosphorus was found to contain 16.2% P, 34.3% 0,and 4.33% V205.

l-inch diameter wet compacts were prepared as in Example I using variousmixtures of Arkansas Ore (1.58%

. V 0 Chile slag, unoxidized or oxidized ferrophosphorus, and 25 byweight sodium chloride based on the total mix additions of ore, slag andferrophosphorus. The compacts were then subjected to a roast-leachprocess as outlined in Example I. The results obtained are shown inTable 9 which demonstrates that by using oxidized ferrophosphorus, alarge quantity of both slag (greater than 40%) and ferrophosphorus(greater than 12%) can be added to a vanadium-containing ore whilemaintaining excellent V 0 recovery. Thus, an alkaline earth metal-con- 9taining slag can be'used in this inventiverprocess in. place of analkaline-earth compound.

.10 .-a temperature of. about 8004900" zCmfurtherheating theparticulated partially oxidized ferrophosphorus TABLE 9 [Recovery ofvanadium by NaCl roast of mixtures of Arkansas ore, Chile slag andFeP]FeP in charge Chile slag in charge Percent Percent Moles lFeP Chile slagC110, and Percent V205 .(based Wt. ratio (based on MgO/P in Grams onore) Grams slag/FeP ore-wt.) FeP-i-slag -Extraction In tails Oxidized.

EXAMPLE X for about /2 hour to 5 hours to substantially convert Twoseparate samples of ferrophosphorous, one in the amount of 100 grams of48 mesh (Tyler) and the other in the same amount sized -100 mesh, wereplaced in silica dishes to a bed depth of about 4; inch. The sampleswere placed in an electric mufiie furnace set at 700 C. and air wascontinuously passed oved the bed. The samples were removed after 1 hour.The gain in weight, oxidation, of each was about 5% to 8%. Furthertreatment at this temperature of 700 C. failed to significantly increasethe amount of oxidation. The partially oxidized material was easilyremoved from the dishes and was slightly sintered. After pulverizing toabout 100 mesh and replacing the samples in the same dishes, they wereheated in the muflie furnace set at 825 C. for about 3 hours and air wascontinuously passed over the material as before. The resulting samplematerials were over 90% oxidized with a total weight gain of 60% in eachcase.

EXAMPLE XI Samples of 48 mesh and 100 mesh ferrophosphorous as describedin Example X were placed directly in silica dishes in the furnacedescribed in Example X and were heated at 825 C. for 3 hours, withoutany prior treatment. Air was continuously passed over the materialduring heating as in Example X. Both sample materials slagged and fusedas a result of the heating treatment and it was not possible to removethe samples from their. trays.

The above examples are not intended to limit the scope of this inventionin any way and are provided primarly to show how the extraction ofvanadium values from ferrophosphorus and mixtures thereof, can beincreased by using the teachings of this invention.

What is claimed is:

1. A process for recovering vanadium from ferrophosphorus containing thesame comprising the steps:

(a) oxidizing particulated ferrophosphorus with an oxidant in the rangeof about 600-7 50 C. for about 15 minutes to 2 hours to partiallyoxidize the phosphorus therein, subjecting the partially oxidizedferrophosphorus to further particulation and thereafter at thephosphorus therein to phosphate;

(b) adding and mixing an alkaline earth containing material to saidoxidized ferrophosphorus in a mole ratio of the alkaline material to thephosphorus in said oxidized ferrophosphorus of between about 1.0 andabout 2.0;

(c) adding and mixing an alkali metal salt in an amount between about 3%and about 35% by weight based on the weight of said mixture in p (d)roasting said mixture at a temperature between about 700 C. and about1=050 C. for a time period of at least 45 minutes so as to substantiallyconvert the vanadium into a soluble state;

(e) leaching said roasted mixture of step (d) with an aqueous solutionto dissolve the vanadium therein; and

(f) separating the vanadium from the leach liquor of step (e).

2. The process of claim 1 wherein water is added to the mixture of step(c) so as to form a moist compact of all the additives.

3. The process of claim 1 wherein a particulated vanadium-containing oreis added to the oxidized ferrophosphorus in step (a).

4. The process of claim 3 wherein water is added to the mixture of step(c) so as to form a moist compact of all the additives.

5. The process of claim 2 wherein in step (b) said alkalineearth-containing material is selected from at least one of the groupconsisting of calcium carbonate, calcium oxide, magnesium carbonate,magnesium oxide, alkaline earth-containing slags and alkalineearth-containing ores.

6. The process of claim 4 wherein in step (b) said alkalineearth-containing material is selected from at least one of the groupconsisting of calcium carbonate, calcium oxide, magnesium carbonate,magnesium oxide, alkaline earth-containing slags and alkalineearth-containing ores.

7. The process of claim 2. wherein in step (c) said alkaline metal saltis selected from at least one of the group consisting of sodiumchloride, potassium chloride, sodium carbonate and sodium sulfate.

8. The process of claim 4 wherein in step (c) said alkaline metal saltis selected from at least one of the group consisting of sodiumchloride, potassium chloride, sodium carbonate and sodium sulfate.

9. The process of claim 5 wherein said alkaline earthcontaining materialis present in a mole ratio of about 1.5, and said alkaline metal salt ispresent in between about 10% and about 25% by weight of the oxidizedferrophosphorus and the alkaline earth-containing material.

10. The process of claim 6 wherein said alkaline earth containingmaterial is present in a mole ratio of about 1.5, and said alkalinemetal salt is present in between about 10% and about 25% by weight ofthe oxidized ferrophosphorus, vanadium-containing ore and the alkalineearth-containing material.

11. The process of claim 9 wherein in step (d) said roasting is carriedout at a temperature of about 875 C. for a period of between about 1 andabout 2 hours.

12. The process of claim 10 wherein in step (d) said roasting is cariedout at a temperature of about 875 C. for a period of between about 1 andabout 2 hours.

References Cited UNITED STATES PATENTS Hermann. Shaw et al. Burwell.Michal. Kunkle. Meyer. Frisk et al. Ekeley et al.

HERBERT T. CARTER, Primary Examiner US. Cl. X.R.

